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NZ Building Code · Fire & AcousticFRR Wall Systems: reading the three numbers
A plain-English guide to Fire Resistance Ratings for NZ walls — what the three numbers mean, when you need one, and why the rating belongs to the whole tested system.
A Fire Resistance Rating (FRR) tells you how long a building element — a wall, floor/ceiling, beam or column — keeps doing its fire job in a standard furnace test (AS 1530.4). For builders it matters because it’s what proves a separating wall, boundary wall or supporting structure will hold up long enough, and it’s expressed as three numbers in minutes.
Where FRRs sit in the Building Code
The Building Code’s fire clauses (C1–C6) are met for houses and small-sleeping uses through C/AS1, and for other buildings through C/AS2. These tell you when an FRR is needed and how big.
Reading the three numbers (e.g. -/60/60)
An FRR is always written as Structural adequacy / Integrity / Insulation, in that order:
- Structural adequacy — minutes the element keeps carrying its load. A dash means it’s non-load-bearing (nothing to fail structurally).
- Integrity — minutes before cracks or gaps let flame or hot gas pass to the cool side.
- Insulation — minutes before the unexposed face gets hot enough (avg +140°C) to ignite things touching it.
So -/60/60 means non-load-bearing, holds flame for 60 minutes and limits heat for 60 minutes — a typical separating wall. 60/60/60 means a load-bearing wall doing all three for 60 minutes.
When you actually need an FRR
- Close to a boundary — external walls near a relevant boundary (within 1 m) limit fire spread to the neighbour.
- Between household units or firecells — separating (intertenancy) walls and floors in duplexes, terraces and apartments.
- Protecting exitways and structure that supports a fire-rated element.
An FRR is a SYSTEM rating, not a product rating
The rating belongs to the whole tested assembly — board type and number of layers, stud size and spacing, insulation, screw pattern and joint treatment. Swap any component (thinner board, wider screw centres, no cavity insulation) and the rating is void.
Build exactly to the manufacturer’s tested system sheet (GIB GBT/GBTL, USG, Speedpanel etc.) and keep it on site for the inspector.
Plain-English guide, not advice. This page helps you understand and navigate the rules — it is general information, not design, engineering or consent advice, and it does not reproduce the copyrighted tables of NZS 3604 or any Standard. Always check the current Standard or Acceptable Solution and your BCA, and use a suitably qualified LBP, engineer or QS where it matters.
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Common questions
What do the three numbers in an FRR mean?
They are always written Structural adequacy / Integrity / Insulation, in minutes. Structural adequacy is how long the element keeps carrying its load (a dash means non-load-bearing), Integrity is how long before cracks or gaps let flame or hot gas through, and Insulation is how long before the unexposed face gets hot enough (avg +140°C) to ignite things touching it.
When does a wall actually need a Fire Resistance Rating?
You need an FRR close to a boundary (external walls within 1 m of a relevant boundary, to limit spread to the neighbour), between household units or firecells (separating/intertenancy walls and floors in duplexes, terraces and apartments), and where you’re protecting exitways or structure that supports a fire-rated element.
Can I swap a component in a fire-rated wall if it seems equivalent?
No. An FRR is a system rating, not a product rating — it belongs to the whole tested assembly, including board type and layers, stud size and spacing, insulation, screw pattern and joint treatment. Swap any component (thinner board, wider screw centres, no cavity insulation) and the rating is void. Build exactly to the manufacturer’s tested system sheet.
Which Building Code documents cover fire and FRRs?
The Building Code’s fire clauses are C1–C6. They’re met for houses and small-sleeping uses through C/AS1, and for other buildings through C/AS2. These Acceptable Solutions tell you when an FRR is needed and how big it has to be, and ratings come from the standard furnace test AS 1530.4.
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